The present invention relates to a hydraulic control apparatus for a construction machine such as a hydraulic excavator, a wheel loader or a crane.
A hydraulic excavator which is a kind of a construction machine includes a lower traveling unit, an upper revolving unit disposed for revolving motion on the upper side of the lower traveling unit and a working apparatus provided on the upper revolving unit for carrying out several kinds of operation. Several kinds of hydraulic actuators for driving the lower traveling unit, upper revolving unit and working apparatus, particularly, a traveling motor for causing the lower traveling unit to travel, a revolving motor for revolving the upper revolving unit with respect to the lower traveling unit and hydraulic cylinders (a boom cylinder, an arm cylinder, and a bucket cylinder) for driving the working apparatus to work are mounted on the hydraulic excavator.
The hydraulic actuators described above are operated by an operation lever disposed in an operator cab, and normally, the actuation velocity of each hydraulic actuator is determined in response to the operation amount of the operation lever. Accordingly, in the prior art, where the operator wants to operate each hydraulic actuator with a fixed velocity, the operator keeps the operation lever at a fixed position, but, where the operator wants to accelerate the actuation velocity of the hydraulic actuator, operation of the operation lever is performed such that the operation amount thereof is gradually increased.
However, the liking for an operation characteristic of the hydraulic actuators is different among different operators. Therefore, it cannot absolutely be said that such an operation characteristic that the actuation velocity of the hydraulic actuator corresponds to the operation amount of the operation lever as in the prior artisan optimum operation characteristic to all operators. Further, it is considered that the liking for the operation characteristic maybe different, even if the same operator operates, depending upon the hydraulic actuator to be operated, and further, even if the same operator operates the same hydraulic actuator, depending upon the working situation thereof.
The present invention has been made in the light of such a subject as described above, and it is an object of the present invention to provide a hydraulic control apparatus for a construction machine by which an operation characteristic of a hydraulic actuator can be changed in accordance with liking of an operator.
In order to achieve the object described above, a hydraulic control apparatus for a construction machine of the present invention comprises, in addition to a target velocity table in which target actuation velocities of a hydraulic actuator corresponding to operation amounts of an operation member to be operated by an operator are stored, a target acceleration table in which target actuation accelerations of the hydraulic actuator corresponding to the operation amounts of the operation member are stored such that one of the target velocity table and the target acceleration table can be selected by operation of a selection switch by the operator. Further, by control means, a target value corresponding to the operation amount of the operation member is set using the table selected by the selection switch to control, based on the set target value, a control valve for controlling a pressure oil supplying amount from a hydraulic pump to the hydraulic actuator.
By the configuration just described, the operator can optionally select, by operating the selection switch, one of such control that the actuation velocity of the hydraulic actuator is adjusted based on the operation amount of the operation member and such control that the actuation acceleration of the hydraulic actuator is adjusted based on the operation amount of the operation member, and as a result, the operation characteristic of the hydraulic actuator can be easily changed in accordance with the liking of the operator. Further, vibration of the hydraulic actuator can be suppressed to improve the operation performance, and as a result, injurious vibration can be prevented to reduce the fatigue of the operator.
Preferably, the control means described above is configured such that a first signal correlating to the actuation velocity or the actuation acceleration of the hydraulic actuator is detected by first signal detection means and the detected first signal is differentiated or integrated by second signal calculation means, and the actuation velocity or the actuation acceleration of the hydraulic actuator different from that of the first signal is calculated. Further, the control means is configured such that, one of the first signal detected by the first signal detection means and the second signal calculated by the second signal calculation means is selected in an interlocking relationship with the selection of the selection switch and is compared with the target value by comparison means, and a control signal for controlling the control valve is produced by control signal production means (a proportional circuit, a proportional integrating circuit, a proportional integrating and differentiating circuit or the like) based on a comparison signal from the comparison means.
By the configuration described above, if one of the actuation velocity and the actuation acceleration of the hydraulic actuator is detected, then both of feedback control based on the actuation velocity and feedback control based on the actuation acceleration can be carried out, and as a result, a sensor or the like for the feedback control based on the actuation acceleration need not be newly provided. In particular, if only software is modified, then the operation characteristic of the hydraulic actuator can be adapted to the liking of the operator.
In this case, preferably the control means described above includes a band-pass filter for passing a vibration component signal only of a characteristic frequency of pressure vibration of the hydraulic actuator and frequencies around the characteristic frequency but cutting a DC component from within the comparison signal, a high-pass filter for extracting a positive vibration component signal from the vibration component signal having passed through the band-pass filter, a low-pass filter for extracting a negative vibration component signal from the vibration component signal having passed through the band-pass filter, and control signal correction means for correcting the control signal using the signal from the high-pass filter and the signal from the low-pass filter. With the hydraulic control apparatus, vibration components in the control signal can be suppressed and attenuated in a positive manner.
Preferably, the selection switch is configured such that the target velocity table can be selected as a basic table but the target acceleration table can be selected when necessary by the selection switch. As a control method of the hydraulic actuator, such a control method that the actuation velocity is adjusted in response to the operation amount of the operation member is commonly used. Therefore, with such a configuration as described above, a sense of incongruity when the operator transfers from some other construction machine to a construction machine to which the present invention is applied can be eliminated, and further, also an operation miss arising from a change of the operation characteristic can be prevented.